1. Field of the Invention
The present invention relates to an air-cooled discharge tube for an ion laser having cooling disks arranged coaxially of the discharge tube.
2. Description of the Prior Art
A discharge tube is disclosed in U.S. Pat. No. 3,753,144 in which between each cooling disk is mounted a ceramic tube so that heat is carried from the region of the discharge channel by the cooling disks. The ceramic tubes are of a significantly larger diameter than the discharge channel and are partially protected by shieldings in the form of bushing protrusions against direct irradiation from the discharge channel.
The disclosed structure, however, can only be used for moderate power lasers since the heating caused by the cooling disks of good thermally conductive material, such as copper, causes mechanical stresses which can lead to fracturing of the ceramic insulator tubes. Furthermore, intense heating of the ceramic tubes occurs even if cooling disks are used that have a coeffecient of thermal expansion matched to that of the ceramic tubes since heating of the ceramic tubes leads to maladjustment of the mirrors of the resonator cavity, resulting in a reduction of the laser power, particularly if different regions of the circumference of the ceramic tubes are cooled differently. Deflection of the laser beam, as well as a greater amount of scattering, leads to a reduction in the measured laser power since laser power is usually measured only in a narrowly limited area around the optical axis of the laser.
There is a demand for extremely stable execution of a laser tube and, thus, for larger diameter insulator tubes. However, this leads to nonuniform cooling of the insulator tubes, especially for air-cooled tubes, which results in different expansions of the insulator tubes causing deflection of the laser beam. Some of the difficulties can be overcome by using BeO ceramic to form the insulator tube. However, BeO is expensive and requires special precautionary measures due to its toxicity.